The invention relates to a side channel compressor, comprising an inlet port for gas and an outlet port for compressed gas as well as a side channel which provides a flow connection between the inlet port and the outlet port, the cross-section of the side channel diminishing between the inlet port and the outlet port.
Such a side channel compressor is known from DE 197 08 952 A1. In this side channel compressor, the cross-section of the side channel tapers continuously from the inlet port to the outlet port. The taper is intended to increase the efficiency of the side channel compressor, in that a constant raise in pressure in the side channel and an increase in the volume flow are produced. According to this prior art, the cross-section of the side channel is rectangular, but has rounded edges.
It is the object of the invention to achieve a side channel compressor with an improved efficiency.
This is achieved in a side channel compressor of the type initially mentioned in that the side channel has at least one section in which it has a cross-section in the form of a half ellipse and in which the maximum depth of the channel continuously diminishes towards the outlet port.
In the side channel compressor according to the invention, the flow conditions in the side channel are optimized in that the transition points of the wall sections delimiting the cross-section are designed so as to be very smooth, so that transition points in the proper sense are not present. This is achieved by the elliptical shape of the channel. The gas flows from the blades of the compressor with an axial speed component, in relation to the blade axis, into the side channel and is deflected therein without leading to extreme losses. Thereby, a higher volume flow and a higher output of the compressor are achieved. Due to the slanted portions associated with an elliptical design, the latter results in a better producibility of the channel by means of casting in sand or diecasting methods.
The section of the side channel with elliptical cross-section may extend along the entire length of the side channel, or only along a part of it. The section with elliptical cross-section should begin at the latest at approximately half the distance of the flow path between the inlet port and the outlet port. It is in this region, namely, that the gas to be compressed has experienced a substantial compression already, to which the cross-section should be adapted by it being reduced.
The section with elliptical cross-section should end in the region of the outlet port, where also the highest compression exists.
It is to be emphasized that the optimum output of the compressor can only be achieved by adapting the diminution of the cross-section of the side channel to the type of gas and the capacity of the compressor, in particular the speed of it. It is, for instance, not optimum if the cross-section diminishes extremely high or too less, because the gas flow is blocked in the first case and in the second case the compressibility of the gas is not fully made use of. The cross-sectional area of the side channel in the section with elliptical cross-section is, according to the preferred embodiment, adapted to the ratio of the increase in density of the gas, by the cross-sectional area being correspondingly reduced. An optimum diminution of the cross-sectional area is produced on the assumption of an approximately adiabatically isentropic compression of the gas to be compressed, the cross-sectional area being reduced corresponding to the diminishing volume of gas.
This course is calculated as follows, with index 1 marking the specific quantities at the inlet and index 2 the specific quantities at the outlet of the side channel.
For the course of compression along the side channel there is true:
m1=m2=const.
With the ideal gas equation: pV=m RT follows                     P        1            ⁢              V        1                    T      1        =                    P        2            ⁢              V        2                    T      2      
or       V    2    =            V      1        ·                  P        1                    P        2              ·                            T          2                          T          1                    .      
With the additional condition {overscore (C1)}={overscore (C2)}= const.
one obtains:       A    2    =            A      1        ·                  P        1                    P        2              ·                            T          2                          T          1                    .      
For an adiabatically isentropic compression and on the assumption:
"khgr"=1,4
xcex94p=200 mbar
P1=970 mbar
T1=20xc2x0 C.
there is true:       T    2    =            T      1        ·                  (                              P            2                                P            1                          )                              x          -          1                x            xe2x80x83T1=(20+273)K=293 K.
For pressure operation follows:       T    2    D    =            293      ⁢              xe2x80x83            ⁢              K        ·                              (                                          200                +                970                            970                        )                                0.4            1.4                                =          309      ⁢              xe2x80x83            ⁢              K        .            
For suction operation follows:       T    2    V    =            293      ⁢              xe2x80x83            ⁢              K        ·                              (                          970              770                        )                                0.4            1.4                                =          312      ⁢              xe2x80x83            ⁢              K        .            
From that follows, in pressure operation, a cross-sectional ratio of the channel between outlet and inlet port:       A2    A1    =                    P1        P2            ·              T2        T1              =                            970                      970            +            200                          ·                  390          293                    =              87        ⁢        %            
and in suction operation a cross-sectional ratio:       A2    A1    =                              970          -          200                970            ·              312        293              =          85      ⁢      %      
With the above formulas, the optimum cross-sectional areas at any desired place of the channel can be determined.
The optimization of the course of the taper of the cross-sectional area along the length of the side channel on the assumption of an adiabatically isentropic compression is not necessarily limited to the elliptical cross-sectional shape of the channel. Rather, this corresponding diminution of the cross-section may also result in an optimization of the efficiency with other channel shapes.
There may be conceivable other constitutional changes of gas in a side channel compressor, for instance an isothermal compression, but the adiabatically isentropic compression has proved to be successful in this context for achieving a high efficiency.
A further design of the invention provides for that the side channel has a semicircular cross-section before the section with elliptical cross-section. This semicircular cross-section changes steadily into an ellipse becoming more and more shallow, with preferably the main axis of the ellipse lying substantially in the flat surface of that cover of the side channel compressor which comprises the side channel.
For reasons in terms of fluid technics, it may be an advantage if the main axis of the ellipse lies slightly inwardly of the cover of the side channel compressor which comprises the side channel.
The width of the side channel should preferably remain constant along its entire length, so that the diminution of the cross-section is effected exclusively by the diminished depth, but with the shape of the ellipse adapted.
According to one design of the invention, the side channel runs, as seen in a side view, in the shape of a horse shoe, so that a large length of the side channel is produced. Prolongations at the ends of the channel constitute the inlet and outlet ports, respectively.
The side channel compressor according to the invention may be configured one-stage or multi-stage, the cross-sectional area of the inlet port of a succeeding stage preferably corresponding to the cross-sectional area of the outlet port of the directly preceding stage. With this, it is to be prevented that the gas experiences a constitutional change in the channel between successive stages.
Preferably, the individual stages are all provided with a side channel as defined above, i.e. with a continuously diminishing cross-sectional area between inlet port and outlet port. As the pressure profile in a multi-stage compressor differs from that of a single-stage compressor, the diminution of the cross-sectional area has, of course, to be adapted to this effect. So there would be necessary for each stage in the two-stage compressorxe2x80x94with equal raise in pressure between inlet and outlet of a two-stage and a single-stage compressorxe2x80x94only half of the channel taper as compared with the single-stage compressor.